Supercritical water oxidation (SCWO) processes can be used to destroy liquid or slurry organic waste streams, especially low volume organic waste streams. SCWO processes take advantage of the unique properties of water at conditions near and beyond the thermodynamic critical point of water (705° F. and 3206 psia). Above the critical point, water has the characteristics of a very dense gas. Organic materials and gases are miscible in this dense water vapor. Thus, above the critical point, liquid or slurry organic waste streams can be readily oxidized and destroyed with very high efficiency.
SCWO processes are well-known in the art. For example, U.S. Pat. Nos. 2,944,396, 4,543,190, 5,387,398, 5,405,533, 5,501,799, 5,560,822, 5,804,066, 6,054,057, 6,056,883, 6,238,568, 6,519,926, 6,576,185, 6,709,602 and 6,773,581, the entireties of which are incorporated herein by this reference, describe various forms of SCWO processes.
In a typical SCWO process, a feed stream containing water and an organic waste material is pressurized, mixed with an oxidizer and caused to react in a plug flow reactor. Thermal energy produced by the oxidation reactions provides the necessary preheat for the reactants. If the feed streams have an inadequate heating value, supplemental fuel is added or the feed streams are preheated. The reactor is designed to provide the required residence time (typically less than about one minute) at supercritical conditions.
Unfortunately, SCWO processes of the prior art are unduly expensive to operate and maintain. For example, depending upon the feed stream, a consumable reactor liner may be required to protect the interior reactor walls from the highly corrosive combustion process and the resulting reaction products. Such a liner may need to be replaced as frequently as every 60-70 hours of operation, resulting in considerable maintenance and operating costs associated with the resulting down time. Other significant costs associated with prior art SCWO processes are the capital costs and operating costs required in providing compressed oxygen or compressed air at 3500-4000 psig. Typically, the operating costs involved in operating air compressors for a SCWO reactor account for greater than 90% of the total operating cost.
Another cost associated with prior art SCWO processes is the large amount of aqueous reaction products produced in the process. Typically such aqueous reaction products present an expensive problem to the operator of the process. Moreover, reaction product salts tend to precipitate out in down stream equipment resulting in the fouling of such equipment, requiring frequent and expensive maintenance to remove such salts.
Accordingly, there is a need for a SCWO process which avoids or minimizes the aforementioned problems in the prior art.